Sea level is the base level for measuring elevation and depth on Earth. Mean sea level (MSL) is an average surface level of one or more of Earths coastal bodies of water from which heights such as elevation may be measured. The global MSL is determined by averaging the values of MSL in respect to the land over a period of time such that changes due to, for example, the tides, also have zero mean.

The height above mean sea level is a measure of the vertical distance of a location in reference to a historic mean sea level taken as a vertical datum. In the metric system, it is formalized as orthometric heights and is called "metres above mean sea level".

Therefore, sea level is not measured in meters, but rather it is used as a reference point to measure the height or depth of a location above or below it.